1. Field of the Invention
The present invention relates to water-bearing explosives which contain an aqueous solution of at least one salt of an inorganic oxidizing acid as a dispersed phase within a continuous organic fuel phase, and to a method of preparing such explosives.
2. Description of the Prior Art
Water-bearing explosives in the form of semi-solid colloidal dispersions are available in film-wrapped cartridges or bags, as well as in bulk form for pouring or pumping into boreholes. In the water gel or slurry type of water-bearing explosive, a solid or liquid fuel is dispersed or dissolved in a continuous thickened or gelled aqueous solution of an inorganic oxidizing salt. In the water-in-oil emulsion type, an aqueous solution of an inorganic oxidizing salt is a discontinuous phase dispersed in a continuous carbonaceous fuel or oil phase.
In U.S. Pat. No. 3,447,978, Bluhm describes emulsion blasting agents in which the continuous phase is a carbonaceous fuel component which forms a water-in-oil type emulsion with an aqueous ammonium nitrate solution component when a water-in-oil type emulsifying agent is present, and which has a gas occlusion temperature of 21.degree.-88.degree. C. The firmness of Bluhm's emulsion system is said to be variable depending on the physical consistency of the carbonaceous fuel used, the latter being required to be thick enough to prevent an occluded gas sensitizing component from agglomerating and being expelled from the emulsion at ambient temperature, yet sufficiently fluid at manufacturing temperatures to permit formation of the emulsion. Bluhm's carbonaceous fuel component must have the ability to provide this consistency differential with variations in temperature.
Bluhm's fuel component becomes thinner when heated and thicker when cooled. After this fuel component has been thinned to a liquid by heating and the emulsion allowed to form, the thickened consistency of the emulsion needed for gas retention is achieved by cooling. If insufficient gas has been occluded, the emulsion is heated again (and thinned) for the introduction of additional quantities of gas, and the final thickened consistency is achieved by cooling. Bluhm achieves this temperature-responsive consistency differential by using an all-wax carbonaceous fuel component, or wax and oil, wax and a polymeric material, or wax and a polymer-modified oil. While the emulsion can be a deformable paste or solid at storage temperatures, varying from very soft to firm depending especially on the physical consistency of the carbonaceous fuel used, the degree of softness or firmness of the water-in-oil emulsion explosives of the prior art has been temperature-dependent and hence subject to variation with changing ambient conditions.
Although film-packaged water-bearing explosives are easy to handle and load into boreholes, in some circumstances there is need for water-bearing explosive charges that are per se self-supporting and preferably rigid, i.e., substantially non-deformable or non-slumping when, without rigid confinement, and even upon exposure to elevated temperatures, they are stacked in storage or in a column loaded in a borehole, or are loaded in an irregularly shaped borehole. Such rigidity is especially important, for example, in primers for blasting agents. Primers are very high-energy, usually compact, explosive products which are used to initiate the detonation of adjacent non-cap-sensitive blasting agents in boreholes, e.g., adjacent chub cartridges or a detonable mixture of ammonium nitrate and fuel oil (ANFO). One type of primer in common use is a packaged cylindrical charge of castable explosive weighing 0.45 kilogram or less and designed to be detonated by detonating cord or a blasting cap. Primers this small in size need rigidity to assure satisfactory performance. Preferably, rigidity is present in the explosive charge itself so that rigid containment is not required. Heretofore, water-bearing blasting agents used in primer cartridges have been non-self-supporting, non-rigid compositions. Co-pending, co-assigned U.S. patent application Ser. No. 27,882. filed Apr. 6, 1979, describes a primer cartridge of this kind.
Even for non-primer uses, self-supportability or rigidity, and the absence of thermoplasticity, in a water-bearing explosive are desirable from the point of view of product stability during storage and use as it may be affected by such variables as temperature, pressure, and ambient moisture.